Integrated circuits are very complex devices that include multiple layers. Each layer may include conductive material, isolating material while other layers may include semi-conductive materials. These various materials are arranged in patterns, usually in accordance with the expected functionality of the integrated circuit. The patterns also reflect the manufacturing process of the integrated circuits.
Integrated circuits are manufactured by complex multi-staged manufacturing processes. During this multi-staged process resistive material is (i) deposited on a substrate/layer, (ii) exposed by a photolithographic process, and (iii) developed to produce a pattern that defines some areas to be later etched.
Various metrology, inspection and failure analysis techniques evolved for inspecting integrated circuits both during the fabrication stages, between consecutive manufacturing stages, either in combination with the manufacturing process (also termed “in line” inspection techniques) or not (also termed “off line” inspection techniques). Various optical as well as charged particle beam inspection tools and review tools are known in the art, such as the VeraSEM™, Compluss™ and SEMVision™ of Applied Materials Inc. of Santa Clara, Calif.
Manufacturing failures may affect the electrical characteristics of the integrated circuits. Some of these failures result from unwanted deviations from the required dimensions of the patterns. A “critical dimension” is usually the width of a patterned line, the distance between two patterned lines, the width of a contact and the like.
One of the goals of metrology is to determine whether the inspected structural elements include deviations from these critical dimensions. This inspection is usually done by charged particles beam imaging that provide the high resolution required to measure said deviations.
A typical measured structural element is a line that has two opposing sidewalls. The measurement of the bottom width of the line involves measuring the top width of the line as well as measuring its sidewalls. Another typical measured structural element is a contact or a hole to be filled with conductive materials. Said structural element is also referred to as via. Vias are usually elliptical or round.
A typical measurement process has multiple stages, including locating a certain feature, scanning the feature to provide an image, processing the image to locate edges and measuring critical dimensions based upon the relative location of the edges. There is a growing need to improve the measurement process.